title: Transverse connectors providing increased stability to the cervical spine rod-screw construct: an in vitro human cadaveric study.
abstract: OBJECTIVE
  The object of this study was to determine if the addition of transverse connectors (TCs) to a rod-screw construct leads to increased stabilization of the cervical spine.
  
  
  METHODS
  Eleven human cadaveric cervical spines (C2-T1) were used to examine the effect of adding connectors to a C3-7 rod-screw construct in 3 models of instability: 1) C3-6 wide laminectomy, 2) wide laminectomy and 50% foraminotomy at C4-5 and C5-6, and 3) wide laminectomy with full medial to lateral foraminotomy. Following each destabilization procedure, specimens were tested with no TC, 1 TC between the C-5 screws, and 2 TCs between the C-4 and C-6 screws. Testing of the connectors was conducted in random order. Specimens were subjected to ± 2 Nm of torque in flexion and extension, lateral bending, and axial rotation. Range of motion was determined for each experimental condition. Statistical comparisons were made between the destabilized and intact conditions, and between the addition of TCs and the absence of TCs.
  
  
  RESULTS
  The progressive destabilization procedures significantly increased motion. The addition of TCs did not significantly change motion in flexion and extension. Lateral bending was significantly decreased with 2 connectors, but not with 1 connector. The greatest effect was on axial rotation. In general, 2 TCs were more restrictive than 1 TC, and decreased motion 10% more than fixation alone.
  
  
  CONCLUSIONS
  Regardless of the degree of cervical destabilization, 1 or 2 TCs decreased motion compared with rods and screws alone. Axial rotation was most affected. Transverse connectors effectively increase the rigidity of rod-screw constructs in the cervical spine. Severe cervical instability can be overcome with the use of 2 TCs, but in cases in which 2 cannot be used, 1 should be adequate and superior to none.
authors.affiliation: Biomechanics Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Miranda N
authors.initials: MN
authors.lastname: Shaw
authors.forename: Etienne P
authors.initials: EP
authors.lastname: Morel
authors.forename: P Andrew
authors.initials: PA
authors.lastname: Utter
authors.forename: Yazeed M
authors.initials: YM
authors.lastname: Gussous
authors.forename: Lise
authors.initials: L
authors.lastname: Ginoux
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Berglund
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Gay
authors.forename: William E
authors.initials: WE
authors.lastname: Krauss
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D006801:Humans; D016268:Internal Fixators; D007796:Laminectomy / Q000295:instrumentation*; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000295:instrumentation*